Sensor placement for fault location identification in water networks: A minimum test cover approach

This paper focuses on the optimal sensor placement problem for the identification of pipe failure locations in large-scale urban water systems. The problem involves selecting the minimum number of sensors such that every pipe failure can be uniquely localized. This problem can be viewed as a minimum test cover (MTC) problem, which is NP-hard. We consider two approaches to obtain approximate solutions to this problem. In the first approach, we transform the MTC problem to a minimum set cover (MSC) problem and use the greedy algorithm that exploits the submodularity property of the MSC problem to compute the solution to the MTC problem. In the second approach, we develop a new \textit{augmented greedy} algorithm for solving the MTC problem. This approach does not require the transformation of the MTC to MSC. Our augmented greedy algorithm provides in a significant computational improvement while guaranteeing the same approximation ratio as the first approach. We propose several metrics to evaluate the performance of the sensor placement designs. Finally, we present detailed computational experiments for a number of real water distribution networks

Seeing the invisible: from imagined to virtual urban landscapes

Urban ecosystems consist of infrastructure features working together to provide services for inhabitants. Infrastructure functions akin to an ecosystem, having dynamic relationships and interdependencies. However, with age, urban infrastructure can deteriorate and stop functioning. Additional pressures on infrastructure include urbanizing populations and a changing climate that exposes vulnerabilities. To manage the urban infrastructure ecosystem in a modernizing world, urban planners need to integrate a coordinated management plan for these co-located and dependent infrastructure features. To implement such a management practice, an improved method for communicating how these infrastructure features interact is needed. This study aims to define urban infrastructure as a system, identify the systematic barriers preventing implementation of a more coordinated management model, and develop a virtual reality tool to provide visualization of the spatial system dynamics of urban infrastructure. Data was collected from a stakeholder workshop that highlighted a lack of appreciation for the system dynamics of urban infrastructure. An urban ecology VR model was created to highlight the interconnectedness of infrastructure features. VR proved to be useful for communicating spatial information to urban stakeholders about the complexities of infrastructure ecology and the interactions between infrastructure features.https://doi.org/10.1016/j.cities.2019.102559Published versio

Modeling the Effect of Oceanic Internal Waves on the Accuracy of Multibeam Echosounders

When ray bending corrections are applied to multibeam echosounder (MBES) data, it is assumed that the varying layers of sound speed lie along horizontally stratified planes. In many areas internal waves occur at the interface where the water’s density changes abruptly (a pycnocline), this density gradient is often associated with a strong gradient in sound speed (a velocline). The internal wave introduces uncertainty into the echo soundings through two mechanisms: (1) tilting of the velocline, and (2) vertical oscillation of the velocline’s depth. A model has been constructed in order to examine how these effects degrade the accuracy of MBES measurements. The model numerically simulates the 3D ray paths of MBES soundings for a synthetic flat seafloor, as though the soundings have been collected through a user-defined internal wave. Along with sound speed information, the ray paths are used to estimate travel times which are then utilized as inputs for a conventional 2D ray trace. The discrepancy between the 3D and 2D ray traced solutions serve as an estimate of uncertainty. The same software can be extended to model the expected anomalies associated with tidal fronts and other phenomena that result in significant tilting or oscillation of the velocline. A case study was undertaken using observed internal wave parameters on the Scotian Shelf. The case study examines how survey design parameters such as line spacing, direction of survey lines, and water column sampling density can influence the uncertainty introduced by internal waves. In particular, an examination is undertaken in which 2D ray tracing models are augmented with MBES water column imaging of the velocline. The investigation shows that internal waves have the potential to cause vertical uncertainties exceeding IHO standards and that the uncertainty can potentially be mitigated through appropriate survey design. Results from the case study also indicate that acoustic tracking of the velocline has the potential to counteract the effects of internal waves through augmentation of 2D ray tracing models. This technique is promising, however, much more research and field testing is required to ascertain the practicality, reliability and repeatability of such an approach

Safe Robotic Grasping: Minimum Impact-Force Grasp Selection

This paper addresses the problem of selecting from a choice of possible grasps, so that impact forces will be minimised if a collision occurs while the robot is moving the grasped object along a post-grasp trajectory. Such considerations are important for safety in human-robot interaction, where even a certified "human-safe" (e.g. compliant) arm may become hazardous once it grasps and begins moving an object, which may have significant mass, sharp edges or other dangers. Additionally, minimising collision forces is critical to preserving the longevity of robots which operate in uncertain and hazardous environments, e.g. robots deployed for nuclear decommissioning, where removing a damaged robot from a contaminated zone for repairs may be extremely difficult and costly. Also, unwanted collisions between a robot and critical infrastructure (e.g. pipework) in such high-consequence environments can be disastrous. In this paper, we investigate how the safety of the post-grasp motion can be considered during the pre-grasp approach phase, so that the selected grasp is optimal in terms applying minimum impact forces if a collision occurs during a desired post-grasp manipulation. We build on the methods of augmented robot-object dynamics models and "effective mass" and propose a method for combining these concepts with modern grasp and trajectory planners, to enable the robot to achieve a grasp which maximises the safety of the post-grasp trajectory, by minimising potential collision forces. We demonstrate the effectiveness of our approach through several experiments with both simulated and real robots.Comment: To be appeared in IEEE/RAS IROS 201